This invention relates to fume hoods utilizing a supplemental air supply and, in particular, to such devices employing horizontally movable sashes.
Fume hoods are conventionally employed in laboratories to contain apparatus and chemicals, particularly those which emit dangerous or noxious fumes. Frequently, legal codes require a face air velocity of the order of 100 feet per minute or greater, which results in the withdrawing of a considerable amount of air from the room in which the hood is located. Since laboratories are generally air conditioned, the waste of the high cost treated air must be kept at a minimum to guard against the high installation costs and operational expenses of heating and air conditioning systems.
To overcome this, it has been the practice to supply such hoods with a supplemental air supply of non-conditioned air. This introduces a complication in that the non-conditioned air must be fed to the fume hood in such a manner as to not affect to any significant degree the conditioned air in the room. Further, the air handling arrangement should advantageously taken into account the fact that a percentage of room air is generally required to be discharged to the atmosphere.
Heretofore, fume hoods have been built which overcome some of the enumerated problems but they have employed vertically moving sashes, which in their open position serve as baffle members. A disadvantage of the vertically moving sashes is that, frequently, apparatus is kept in the hood which require adjustments along a vertical section. For example, the apparatus may be only 1 foot wide by 3 feet high, but, with a conventional vertically movable and operating sash, the same may open some 16 square feet of sash space to permit the operator or technician to adjust the equipment.
By employing a plurality of overlapping horizontally movable sashes a normally 5 feet wide opening is inherently reduced by fifty percent or more permitting a comparable percentage reduction in loss to the building heat and air conditioning system. In research centers that employ hundreds of fume hoods, the savings in energy can be substantial. The design further provides greater protection to the technician, since it can reduce the exposure to operations within the hood to a minimum and permits each horizontal sliding sash to be used as a safety shield.